There are many different methods for locating leaks in pipelines, including those methods which are based on the variation in temperature when leaks occur. In German patent application DE 30 49 544 A1 sensors in respect of temperature, moisture and radioactivity are arranged between the pipeline wall and the insulation and are connected to an analysis station by way of optical waveguides or fiber optics. Many sensors and accordingly many optical waveguides are needed in order to analyze propagation of the leakage. The handling of such optical waveguides in the ground gives rise to problems.
German patent application DE 195 09 129 A1 describes a further known method and apparatus for checking and monitoring the condition of pipes, containers, vessels, pipelines or the like, wherein local fluctuations in temperature are detected. This involves establishing the ambient temperature distribution over portions of the item to be monitored, and using an elongate temperature sensor for distributed temperature measurement. When a local anomaly is detected in the temperature distribution, it is concluded that there is a leak. For establishing the ambient temperature distribution, use is made of an optical-fiber sensor cable which is operated with laser light, and evaluation in respect of transit time and intensity of the backscattered laser light is implemented. That mode of temperature detection is subject to error sources which vary with time so that reliable evaluation over long periods of time becomes difficult.